from collections import defaultdict
pair=defaultdict(list)
ind=defaultdict(int)
M=int(input())
B=list(map(int,input().split()))
def dfs(S,c):
  if len(S)<=2:
    if len(S)==2:
      a,b=list(S)
      if pair[a^b]!=[]:
        ans=[ind[a],ind[b]]
        for i in pair[a^b]:
          ans.append(i)
        print(len(ans))
        print(*ans)
        exit()
      else:
        pair[a^b]=[ind[a],ind[b]]
    if len(S)==1:
      S=list(S)
      a=S[0]
      if pair[a]!=[]:
        ans=[ind[a]]
        for i in pair[a^b]:
          ans.append(i)
        print(len(ans))
        print(*ans)
        exit()
      else:
        pair[a]=[ind[a]]
  else:
    s0=set()
    s1=set()
    for i in S:
      if (2**c)&i==0:
        s0.add(i)
      else:
        s1.add(i)
    dfs(s0,c-1)
    dfs(s1,c-1)
    
for i in range(M):
  if ind[B[i]]!=0:
    print(2)
    print(ind[B[i]],i+1)
    exit()
  elif B[i]==0:
    print(1)
    print(i+1)
    exit()
  ind[B[i]]=i+1
dfs(set(B),59)
print(-1)